I am in the process of building my kegerator and have room for 2 cornies in it. One of my selling points to SWMBO was that when one of the taps is free, we could keg some soda water to dispense there.

After reading this post, I started to think about how soda is dispensed in bars/restaurants. I never paid attention to how it worked during my years in the restaurant world, but basically it combined c02 and water at the instance of dispensing to make soda water. Could we do this at home and not have to sacrifice a keg? I could easily build a third tap into my tower for this. I attempted to search for mixing valve on here, but did not find anything.

In order to do something like this, I think you need a chiller and carbonator system in place. Kind of like http://www.truetex.com/carbonation.htm which goes through a few details. Particularly the MCCann's carbonator unit.

In order to do something like this, I think you need a chiller and carbonator system in place. Kind of like http://www.truetex.com/carbonation.htm which goes through a few details. Particularly the MCCann's carbonator unit.

Hey thanks Kevin. I had found a similar article on Instructables about the bottle trick and might do that instead. I was just hoping to see if making an instant tap was possible, but not for the price of that Mcanns unit.

Welcome, I had found that article and dug through it before getting my own co2/keg system to find the comparisons between all the different possible systems for water(soda).
Since you have space for 2 kegs, it's probably better to do other carbonated drinks and keep in mind "When a tap is free" isn't going to be likely.

Alternatively, in regards to the bottle trick, rather than building your own, they do sell a molded carbonator cap in different stores for about 15 bucks.
Fortunately, it only takes about a minute to shake up a 2 liter bottle of water. Less for a quick 12 ounce bottle of water for single person use.

I run a 3 corny (ball lock) keg system at home and always have one keg of fizzy water on tap. Before my kegerator I used the carbonation cap and 1L or 2L bottles. Its a bit more than the instructables hack, but worth it in the long run.

The real downside of not having a keg is cleaning and storing empty PET bottles.